1. Field of the Invention
The present invention relates to a trigger switch for a power tool and, more specifically, to a trigger switch for a power tool having improved dustproof properties and waterproof properties so as to endure use in a dusty environment.
2. Prior Art
A trigger switch for a power tool in the prior art includes a trigger 14 on the outside thereof to be operated, a contact mechanism provided in the interior of a case 11 and configured to turn ON and OFF according to the movement of a plunger 22 sliding on the basis of the operation of the trigger 14 and, in addition, a motor connecting terminal 31, a signal terminal 35, and power connecting terminals 33 and 34 to be connected to a motor, a controller, a power source and the like on the outside arranged in a so-called exposed state via a terminal fitting portion 19 as shown in FIGS. 11 to 14. The terminals are configured to secure motor connecting lead wires 41 and 42, power connecting lead wires 43 and 44, and a signaling connection lead wire 45 with solder or screws.
Also, as shown in FIG. 13, the plunger 22 coupled to the trigger 14 is connected to the contact point mechanism in the interior thereof by the intermediary of an internal seal cover 24 provided in the interior of the case 11, and is configured to maintain a state in which the trigger 14 is constantly urged outward by the intermediary of a restoration spring 23 on the outside of the case 11.
Then, a cover 13 is attached to the case 11 provided with the contact point mechanism, and a joint portion between the attached case 11 and cover 13 is bonded by ultrasonic welding, so that improved dustproof properties and waterproof properties are achieved.
Furthermore, as shown in FIG. 14, the plunger 22 coupled to the trigger 14 is configured to be provided with an accordion-type external seal cover 15 on the outside on which the plunger 22 slides, and a restoration spring provided on this portion is stored in the interior of the case 11 not shown. In this manner, with the provision of the external seal cover 15 so as to close an engaging hole of the case 11 for the sliding movement of the plunger 22, entry of dust into the interior of the case 11 generated in association with the sliding movement of the plunger 22 may be prevented.
JP-A-2001-118449 and JP-A-2003-109451 are examples in the prior art.
However, in the switch for a power tool described in the prior art, the improvement of dustproof properties and waterproof properties are achieved by bonding by welding the joint portion between the case and the cover by the ultrasonic welding method when attaching the cover to the case, which is a so-called fitting member formed of a resin component. However, there is a problem that the switch cannot be disassembled after the bonding, and operations such as repair in the process cannot be performed.
There is also a problem that a portion where the cover is in contact with the case is in a rugged and complex shape, and accordingly the bonding effect is not sufficient.
In addition, since a terminal fitting portion cannot be welded by ultrasonic welding at portions of terminals, the bonding is still necessary. Therefore, a method of bonding the terminal fitting portions and terminal root portions with an adhesive agent may be employed. However, there arises a problem that there are many points to be bonded and the bonding operation is troublesome, so that the quality is affected by variations in bonding.
In addition, in a method of using the accordion-type external seal cover for preventing entry of dust or moisture from the plunger coupled to the trigger, in a trigger sliding portion, the external seal cover comes into contact with the plunger and slides in friction against the plunger. Therefore, the engaging hole where the plunger engages cannot be closed completely, and hence the probability of entry of dust or moisture into the interior of the switch still remains.
Therefore, it is necessary to simplify a fitting state of components including a case and a cover, which correspond to a fitting portion of the components and enhance dustproof properties and waterproof properties with minimum points of contact. Also, in a terminal fitting portion, it is necessary to enhance the dustproof properties and the waterproof properties by sealing with an adhesive agent or attaching a separate member such as a rubber seal cover. In addition, in a trigger sliding portion, it is necessary to enhance the dustproof properties and the waterproof properties at the time of operation of a trigger specifically by an external seal cover.